Thermal processing concerns the heat treatment of a heat treatable material (e.g. metal parts). The heat treatable material is heated to a desirable temperature and then cooled at a controlled rate. Thermal processing includes heat treating operations such as sintering, brazing, annealing, carburizing, and the like which require heating of materials to yield a particular material having selected physical properties. Prior to thermal processing, the material is typically formed into a compressed form from a powder in a desired shape or simply pre-casted or pre-formed as a solid piece.
Furnaces are utilized to carry out thermal processing either continuously or batchwise. Continuously operated furnaces have a length, typically of 50 to 100 feet and include a conveyor belt assembly for moving the parts for processing through the furnace. Batch furnaces typically have a shorter length. Such furnaces typically include an entryway for introducing the heat treatable material and an exitway for retrieving the heat treatable material as a finished part. The size of the entrance and exit openings may be adjusted by movable doors to accommodate parts of various sizes and shapes and to maintain the furnace atmosphere therein. The heat treatable material moves through the entryway and is carried within the furnace by the conveyor belt. The to remainder of the furnace is substantially gas-tight and thereby closed to the outside atmosphere.
Within the furnace, the heat treatable material is usually thermally processed in the presence of an atmosphere flowing therethrough. The atmosphere excludes ambient air which may interfere with the thermal processing, and functions as a heat treating gas to initiate a heat treating operation such as metal oxide reduction, carburizing, decarburizing, and the like. In addition, the atmosphere assists in removing undesirable vaporized materials from the thermal processing operation. The undesirable vaporized materials are derived from, for example, lubricants, binders, chemical vehicles, oils and the like. Removal of these materials from the heat treatable material may be performed before the onset of the thermal processing operation.
To remove undesirable vaporized materials before thermal processing, the atmosphere is usually introduced within the furnace in counter-current flow to the movement of the heat treatable material. The undesirable vaporized material which may in part be oxidized by the presence of residual oxygen may therefore be purged before the onset of the thermal processing operation.
Due to competitive and economic pressures, furnace operators typically exceed the rated capacity of a furnace to meet production orders. As a result, the undesirable vaporized materials are not completely oxidized before leaving the furnace creating environmental concerns. In addition, the undesirable vaporized materials may rise to dangerous levels within the furnace and associated exhaust systems thus creating safety and fire hazards. Still further, the undesirable vaporized materials may also remain in the heat treatable material resulting in inferior quality products. The increased production rate may also diminish the capacity of the furnace to properly heat the parts to a desired temperature for enabling complete thermal processing.
It would be of significant advantage in the art of thermal processing to provide a device adapted for association with thermal processing furnaces for increasing production output capacity and improving the quality of exhaust emissions while maintaining a high yield of quality products in a cost effective and energy efficient manner.